Microwave ovens



MICROWAVE OVENS 2 Sheets-Sheet 1 Filed June 5, 1958 training IIIIIIIIIIIIIIIII'E} .3 {a h n mwk INVENTOR. Lou/s H. SCI- ALL A TTORNEKS L. H. SCHALL 2,956,143

MICROWAVE OVENS Oct. 11, 1960 Filed June 5, 1958 2 Sheets-Sheet 2 INVENTOR. Lou/5 H. SCHALL ATTORNEYS 2,956,143 lvncnowavn OVENS Louis H. Schall, Dedham, Mass., assignor to Raytheon This invention relates generally to microwave heating ovens and more specifically to access doors for ovens of this type.

The primary object of this invention is to provide an access door to a metallic radio frequency cavity, which in closed position will not permit any appreciable escape or leakage of microwave energy from the interior of the cavity. 1

A more specific object of this invention is to provide an improved door structure for microwave ovens.

Another object of this invention is to provide an improved energy seal for microwave oven doors.

With the foregoing and other objects in view the invention resides in the following specification and appended claims, certain embodiments and details of construction of which are illustrated in the accompanying drawings in which:

Figure 1 is a front view of an oven according to this invention,

Figure 2 is a vertical section taken along the lines 2-2 of Figure 1,

Figure 3 is a partial horizontal section taken along the lines 3--3 of Figure 1, and

Figure 4 is a view similar to Figure 3 illustrating a modified form of the invention.

In oven-type microwave cooking devices, the problem arises of providing adequate shielding at the door opening to prevent the escape of radio-frequency energy. As the field intensity inside the oven is very high, this may be an important problem, both to minimize radiofrequency interference and to prevent radio-frequency burns to persons who might come in contact with the edge of the oven door. In the prior art it was found that a planar contact type of closure, of such a size that the metallic contact area between the door and the oven is approximately a quarter-wavelength long, is very efiective, giving substantially complete shielding yet being free from sparking. The present invention involves this type of door generally and includes a substantial improvement over the prior art.

Referring more particularly to Figures 1 and 2 an enclosure 10 comprising a cavity 11 is illustrated as having attached thereto a microwave oscillation generator 12 of any desired type such as a magnetron, which when energized will fill the cavity 11 with microwave energy.

Disposed on the bottom wall 13 of the oven 10 is a food tray 14, illustrated in phantom lines, which is adapted to be cooked by the microwave energy of the oven. In order to permit access to the interior of the oven 10 for inserting and removing tray 14, a rectangular aperture 15 is provided in the front wall 16 of the oven 10. As illustrated the aperture 15 is located in an inwardly offset portion 17 of front wall 16 so that a suitable closure for the aperture 15 will lend a flush appearance to the front wall 16 of the oven.

Pivotally supported by a suitable hinge 18 to the lower edge of oven wall 16 is a metal door 19 which in closed position substantially -fills the offset portion 17 of wall 16.

United States Patent preferably of conductive rubber.

The details of construction of the door 19 shown in Figure 1 are illustrated on an enlarged scale in Figure 3. The door 19 comprises a flat sheet metal plate 20 of such an area as to completely close access opening 15 with a marginal overlap contact area at 21 around the entire opening to insure a good electrical shield against the loss of microwave energy from the oven 10. The plate 20 is secured as by rivets 22 or other suitable means to an inner flange 23 of a channel shaped metal member 24 of the door 19. The member 24 comprises an inner angularly directed wall 25 terminating in the flange 23, an outer wall 26 which when door 19 is closed is substantially parallel with the wall 27 of the recess 17, and a bridging wall 28 between the wall 25 and wall 26, which bridging wall is flush with the front wall 16 of oven 10 when door 19 is closed. The hinge 18 is connected between the bridging wall 28 of door 19 and the lower edge of oven wall 16. The wall 26 of door 19 is recessed at 29 over its entire periphery to provide a seat for a continuous seal 30 of compressible conductive material, The seal 30 is held in recess 29 by a suitable adhesive. With the door 19 in closed position the seal 30 is somewhat compressed against the inner wall 27 of oven recess 17.

It will therefore be obvious to one skilled in the art that the door 19 is provided with a double seal against the leakage of microwave energy from the interior of the oven 10. The first seal is provided along the metal contact area 21, and the second seal is provided by the conductive material 30. Tests indicate that the conducting rubber seal 30 should be located at a distance of one inch or more beyond the metal contact area 21 and should be compressed slightly, as illustrated, for best results. The

seal 30 is preferably neither too good nor too poor a conductive material such as conductive rubber or the like, and as such will dissipate any energy leaking past the seal formed at the area 21.

In the modified form of door seal of Figure 4, the wall 16 of oven 10 is provided with a seat 31 in which is secured by a suitable adhesive a seal 32 of conductive rubber or the like. The door 33 is substantially identical to the door 19 of Figure 3 except that wall 26 is provided with an outwardly directed flange 34 which when door 33 is closed bears against the seal 32 compressing the same slightly as the plate 20 engages the metal of the oven along the contact area 21. As in the form of Figure 3, it is therefore obvious that this form of the invention provides a double seal against the leakage of microwave energy from oven 10 with the door 33 in closed position.

It is obvious that the forms of doors or closures illustrated in Figures 3 and 4 may be subject to many detailed modifications. For example in Figure 3 the seal 30 could be seated in the wall 27 instead of being mounted on the door. Likewise in Figure 4 the seal 32 could be door mounted instead of oven mounted. The prime consideration in any modified form is that dual seals are provided about the oven access opening with the second seal being spaced from the first seal.

While the door 19 has been illustrated as being pivotedly secured to the oven it is obvious that the invention is applicable to closures of other types such as friction fit non-secured types. In the hinged form illustrated the hinge 10 is provided with spring means (not shown) to bias the door inwardly against the compressible seal to insure good contact along this seal and along the inner metal contact seal in the area 21. The door 19 is' provided with a handle 35 for the usual purpose of opening and closing the door when inserting or removing objects into or from the oven.

It is to be understood that this invention is not limited to the particular details as described above. as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

I claim:

1. High frequency apparatus comprising .a metallic enclosure, means for supplying high-frequency electromagnetic waves to the interior of said enclosure, said enclosure having an access opening therein, a metallic door for closing said opening, said door, upon closure thereof, being in continuous direct metallic contact with said enclosure outside of said opening over a planar contact area to form a first seal against the loss of energy from within said enclosure and a second continuous seal against the loss of energy from within said enclosure formed of solid conductive rubber spaced from said planar contact area and positioned between said door and said enclosure for continuous engagement therebetween about the opening when the door is in closed position.

2. A microwave heating apparatus comprising a metallic enclosure, means for supplying high-frequency electro magnetic Waves to the interior of said enclosure, said enclosure having an access opening therein, a metallic door for closing said opening, a first continuous seal between the door and the enclosure to seal against energy loss from said enclosure through said opening about the door,

and a second continuous seal of conductive rubber spaced from said first seal and positioned between said door, and said enclosure to dissipate energy leaking past said first seal.

3. A microwave heating apparatus comprising a metallic enclosure, means for supplying high-frequency electromagnetic waves to the interior of said enclosure, said enclosure having an access opening therein, a metallic door for closing said opening, the contact area between the door and the enclosure about the opening constituting a first continuous seal against the loss of energy from within the enclosure, and a second continuous seal of conductive rubber surrounding said first seal and being spaced therefrom to dissipate energy leaking past said first seal.

References Cited in the file of this patent UNITED STATES PATENTS 2,500,676 Hall et a1. Mar. 14, 1950 2,623,981 Anderson et a1. Dec. 30, 1952 2,632,838 Schroeder; Mar. 24, 1953 2,716,694 Schroeder Aug. 30, 1955 2,783,295 Ewing Feb. 26, 1957 2,831,047 Wadey Apr. 15, 1958 2,831,952 Warner Apr. 22, 1958 

